To reduce friction and enable a drawer or sliding device to withstand a heavy load, slides for enclosures such as file cabinets and other furniture employ bearings to reduce wear. Specialized enclosures and furniture for medical, industrial, and engineering applications often requires thin drawers and thin drawer slides. Such applications also require a heavy-duty slide.
In a full-extension slide, two pairs of bearing raceways (bearing travel surfaces) for four sets of ball bearings are usually required to bear a typical load. The use of four separate sets of ball bearings poses obstacles to miniaturization of the slide. Furniture designers desire the slide to be thin in the horizontal or lateral direction, thereby enabling a drawer to be as wide as possible compared to the opening in which it slides. Moreover, designers want slides which are short in the vertical direction to keep the slide unobtrusive and cosmetically attractive, and to enable use with thin drawers.
In most drawer slides of the prior art, the four separate ball bearing assemblies are aligned in pairs on two vertical axes. To make a drawer slide thin in the horizontal direction, designers have focused on making the relative vertical separation of one pair of bearings narrower than the other. This enables the axes of the bearing pairs to become nearly collinear, resulting in a thin slide.
For example, U.S. Pat. No. 5,022,768 (Baxter) discloses, in FIG. 1, a prior art slide mechanism in which the ball bearing pairs are on nearly collinear vertical axes. This results in a vertically tall slide which is expensive to manufacture and very obtrusive when seen on an open drawer. Also, two different sized ball retainers are needed, further increasing cost.
FIGS. 3, 4, and 7 of U.S. Pat. No. 4,469,384 (Fler et al.) discloses a similar collinear axis slide. However, the resulting slide is not symmetrical, requiring separate fabrication of the outer and inner channel members. This increases manufacturing costs. Also, the inner channel member is very narrow, providing little space to mount the large fasteners, bolts or tabs required in a heavy-duty application. Designers desire to provide a slide which reduces manufacturing costs by incorporating symmetrical parts, and which provides a large mounting surface area.
Another approach of the prior art is to use noncollinear bearing pairs in which separate central retainer members serve as raceways for the bearings. For example, FIG. 1 of U.S. Pat. No. 3,712,690 (Fall) discloses a drawer slide comprising inner and outer rails and an intermediate element operatively associated with both rails to permit longitudinal sliding movement along the three major elements. The intermediate element indicated generally by numeral 24 comprises a bar 25 formed to define longitudinal trackways 26 and 27 receiving bearings 15 and 16. An identical, oppositely arranged bar 28 is secured to the bar 25 and provides outwardly opening trackways 29 and 30.
Use of separate bars 25 and 28 make the device of Fall susceptible to bending and twisting stresses. Also, a separate manufacturing operation is needed to fasten the bars 25, 28. Thus, designers of drawer slides desire to provide a slide in which the central slide member is structurally stable, and in which few manufacturing operations are needed.